The history of steel in New Zealand and the evolution of reinforcing steel
The use of steel in New Zealand dates back to the late 19th century. However, several practical limitations meant that keen attempts to smelt or mill the steel were not successful until the mid-20th century.
Due to the basic resources available at the time, the history of steel in New Zealand naturally follows the course of the country’s industrial development and growth in production post-World War II.
Before European settlement in New Zealand, Māori used stone tools and naturally found resources to build shelters and craft materials. European settlers introduced iron tools and weapons which had a significant impact on society and led to advancements in construction.
As early as 1841, explorers found natural deposits of ironsand along the west coast of the North Island. Ironsand and closely related limonite (iron ore) were noted to have traces of iron and attempts were made to extract iron from both resources. However, these attempts were unsuccessful due to the different mineral composition encountered and technological limitations of the time. The amount of iron extracted was not substantial enough to support a steel mill.
The first functioning steel mill was attempted by the Taranaki Iron Works in the early 1900s, but this endeavour was short lived.
Subsequently, the most successful attempt was made by the Otago Iron Rolling Mills Company (OIRM) in Dunedin, which resourcefully sourced local scrap metals and imported semi-processed iron ore. For many years it was the country’s only steel mill but it closed in 1953.
After World War II, there was a significant increase in global demand for steel production. The New Zealand Government committed to developing the country’s steel industry using New Zealand’s source of ironsand.
Starting in the 1940s, the government provided funding and technical expertise to understand the steel milling process. By the early 1960s, New Zealand had a flourishing steel industry, highlighting the importance of establishing a domestic source of steel manufacturing rather than relying on imports.
By 1965, after decades of research and experience with New Zealand’s ironsand and the growing steel industry, New Zealand Steel Limited was formed. The national company was created to continue developing the steel industry using New Zealand’s ironsand and was partly government owned.
New Zealand Steel built the Glenbrook Steel Mill in the Waikato region, a project costing over $40 million, which was completed by 1969. In the 1980s the mill went under a major expansion funded by the government, though the work was somewhat controversial at the time.
The success of this mill was due to the technological advancements in smelting local ironsand. In a world first, New Zealand Steel successfully separated and refined the titania and silica minerals from the iron. This was done by using magnetic equipment and gravity separation processes before refining the mineral into steel using furnaces. Previous attempts had relied only on blast furnaces which failed due to the chemical composition of magnetite ore found in the local ironsand.
These advances were crucial to the efficiency and success of New Zealand’s steel industry. While there are many steel manufacturing plants and smaller foundries around New Zealand, Glenbrook remains the country’s primary steel mill facility, processing 1.2 million tonnes of ironsand ore and producing 650,000 tonnes of steel annually.
Evolution of reinforcing steel
While New Zealand was still working to establish steel mills and process the challenging ironsand minerals, efforts were made to construct buildings using basic reinforced steel concrete methods in the late 19th century. These methods were influenced by developments in Europe and the United States of America and relied heavily on imported steel.
The evolution of reinforcing steel in New Zealand shares many similarities with other countries, especially in terms of global advancements in construction materials, seismic design and sustainability. However, New Zealand’s experience with reinforcing steel differs due to its unique geographic context and experience with seismic activity.
Early structures using reinforced concrete first appeared in infrastructure projects like bridges, dams, and public buildings.
The steel used during this period was typically plain round bars embedded in concrete to provide tensile strength. Early reinforcing practices were basic with limited understanding of steel/concrete bonding and no specific standards.
As urban infrastructure and large buildings grew in cities like Auckland and Wellington, the use of reinforcing steel expanded. In the 1920s, building codes began incorporating guidelines for using reinforcing steel, especially following the 1931 Napier earthquake, which led to the development of one of the most stringent earthquake-resistant building codes in the world.
By the 1950s, the construction industry in New Zealand started following more standardised practices for reinforcing steel, aligning with international norms. This was due to increased awareness of material properties, structural performance and the need for consistent building practices.
During this period, ribbed reinforcing bars began replacing older plain round bars as they were proven to have better bonding properties. These bars offered better anchorage with concrete, improving the tensile performance of reinforced structures.
Research by New Zealand institutions, like the University of Canterbury and the University of Auckland, contributed to the development of more resilient reinforcement techniques that could withstand the dynamic forces of earthquakes.
The demand for high-strength, ductile reinforcing steel grew from the 1950s onwards as modern deformed bars made from higher-grade steel replaced earlier, less ductile bars.
The introduction of higher-strength steel allowed for more efficient designs with reduced bar diameters and spacing, enhancing construction efficiency while maintaining safety.
The introduction of New Zealand Standards for steel reinforcement, such as AS/NZS 4671:2019 (Steel for the reinforcement of concrete) unified the specifications for steel reinforcement in concrete structures across Australia and New Zealand, creating consistencies in the materials and testing requirements in both countries.
The standard ensures that the steel used in concrete construction has the necessary properties to perform well, such as yield strength, tensile strength, ductility and durability.
This AS/NZS 4671 standard was first introduced in 2001 and set a baseline for steel reinforcement construction. It was revised and updated in 2019 to align with current industry practices that reflected the advancements and changes in manufacturing and testing technology.
Following the Canterbury earthquakes in 2010 and 2011, New Zealand revised and strengthened its seismic building codes, particularly concerning the detailing of reinforcing steel in critical structural elements like columns, beams and shear walls. These revisions included stricter requirements for ductile detailing, confinement and the use of high-strength, resilient reinforcing steel.
The failures observed in some Christchurch buildings post-earthquakes prompted the revision of standards for steel-reinforced concrete, particularly regarding ductility, anchorage and the arrangement of reinforcing bars.
The earthquakes also led to increased emphasis on retrofitting older buildings with modern reinforcing techniques – an approach that is not always as prevalent in other regions unless prompted by a disaster.